In a wireless communication system such as LTE, a random access (hereinafter, abbreviated to RA) procedure is executed when a UE establishes a connection with an eNB, when the UE performs reconnection (resynchronization), or the like. The RA procedure includes a contention type RA procedure and a non-contention type RA procedure. The contention type RA procedure can be used for all purposes, and the non-contention type RA procedure is used for specific purposes such as handover. Here, the contention type RA procedure is used.
In the RA procedure, the UE transmits an RA preamble to the eNB, and the eNB returns an RA response to the UE. Then, the UE transmits a control message to the eNB by using an uplink resource allocated through a UL grant in the RA response. The control message is referred to as Message 3 (Non-Patent Document 1).
With respect to Message 3, an RRCConnectionRequest message is transmitted at the time of connection, and an RRCConnectionReestablishmentRequest message is transmitted through common control channel (CCCH) which is a logical channel at the time of reconnection.
The RRCConnectionRequest message and the RRCConnectionReestablishementRequest message are collectively referred to as a CCCH service data unit (SDU) in terms of standard specifications. The size of the RRCConnectionRequest message and the size of the RRCConnectionReestablishmentRequest message are both 48 bits, and 8 bits of an MAC header are added to the messages, and the size of an MAC PDU is 56 bits. Namely, the 56-bit data becomes one Transport Block that can be transmitted through a physical layer (PHY), and the size (56 bits) thereof becomes transport block size (TBS).